Ask what your humidity should be on a forum and you will undoubtedly get at least a dozen different opinions. The only thing that is widely agreed upon is that at lockdown and hatch it needs to be higher.
Why is this?? Because different things work for different people because of various factors that these books and manuals do not take into consideration. The habits of the hatcher, the area that they are in and whether they have a dry or humid atmosphere. The quality of eggs also can play a role. Getting a definite answer is impossible and the issue of humidity can be very confusing. No one is wrong. They have just found what works for them. Some very seasoned hatchers don't even bother with monitoring humidity because they've done it so much they just know what works for them.

So how do you make the confusing understandable? In my opinion the first step is to understand why we control the humidity. An egg needs to loose 13/14% of it's weight during incubation. This weight that it is loosing is actually moisture. Moisture leaves the eggs through the pores of the shell. As the moisture leaves, the air cell in the egg grows. This is very important because when your little chick decides it's time to hatch, he/she is going to pip into the area where the air cell should be. If that air cell is not big enough and there is too much moisture there he/she can drown. On the flip side of that if your air cells grow too big the membrane can “shrink wrap” your chick. This can suffocate them if they have not pipped, if they manage to pip they will be stuck and not be able to move to finish the job.

That's the why of it. Now, the how of it. So how do we know how big the air cells should be? There are many egg pictorials or air cell charts out there. This is the one I use: (I'd give credit to the creator if I knew who that was.)

I believe that there are two ways to go about knowing how to regulate your humidity so that it works for you. Pick a number from 30-50%, (the range you'll find a good majority of hatchers use for the first 17 days.) Start your incubation at that number-but monitor your air cells! Candle your eggs at days 7&14 especially. Mark the air cells with a pencil. If your air cells aren't where they need to be at these times, you still have time to regulate before going into lockdown. Compare what you are seeing to the chart. If your air cells are too small, you know that your humidity is too high. Not enough moisture has left the egg. In this case you need to lower your humidity. (How much depends on the air cell. If it's borderline small, I'd go, 10% less. If it's significantly small, I'd go dry, at least for a couple days and candle after 2 days to see the progress and make the next decision.)

If the air cells are too big then you need to higher the humidity. This will slow down/stop air cell growth and let the development catch up with the air cell size. (Again, how much is going to depend on the discrepancy. Borderline big, raise it 10%. Significantly large, I'd say raise it TO 60% (not raise it 60% more...just up to 60% total,) for a couple days and check to see progress. If they are still growing raise it a bit more.

By keeping track of what your percentages are, you'll have a better idea of what percentage of humidity works for you.

The second way: start with a dry incubation if your incubator holds at least 25% when completely dry. Dry incubation is becoming more and more popular among chicken hatchers. Many people that have had not so great hatches (especially with the cheaper styrofoam incubators) have switched to the dry method and have had better results. I myself run dry when I can. (Seasons have a big impact on humidity levels and running dry. Being in Northern New York with regular below 0 temps and running a pellet stove for heat dries the ambient humidity in my home making it impossible to go completely dry in the winter.)

If your incubator holds at least 25% dry start your incubation &..... monitor your air cells! As long as your air cells are growing at the proper rate, you don't have anything to worry about. If you find that they are growing to fast, higher it, I'd say in increments of 5-10%. Rarely should you find too small air cells doing a dry incubation, providing you aren't in a tropical region.

What about lockdown and hatch??

And there's another question that you are going to get a dozen different answers for. I shoot for 75% many people do prefer a 70-75% range. Many people are happy with the recommended 65% and still there are others that insist 55-60% is perfectly fine for hatching.

More confusion.

Here are my thoughts: Are you a meddler? If you have a chick that you feel needs assisting, (There is an awesome thread on BYC on assisted hatching and why it should only be done if you feel it's absolutely necessary and the what happens if you assist too soon.) are you willing to open the incubator to help?

Many people have a hands off philosophy after lockdown. They will not, for any reason open that incubator until the hatch is complete. If a chick is stuck..so be it. If there are 15 chicks running around and it takes 2 days for the rest to hatch, then those chicks are in there for two days. (There is nothing wrong with their philosophy, but....)

If you are a hands off hatcher, then you can probably successfully hatch out chicks with 60/65% humidity in your bator.

If you are anything like me, then a higher humidity is better for you. I like to move my chicks to the brooder once they are active and bouncing off my incubator walls, thermometers the other eggs and each other. I do not leave my chicks in the bator until hatch is over. If I feel it is absolutely necessary I will assist a hatch. To properly assist a hatch you have to take things slow, help a little and replace the chick in the egg for rest and to give them a chance to finish. This constitutes opening the bator periodically. Every time you open the bator humidity slips out. Chicks need that humidity to hatch. If you are a “meddler” or someone who feels it necessary to open the bator, then naturally a higher humidity level is going to help keep adequate humidity in your bator. So take into consideration your actions and you should be able to judge a good humidity range for hatching. I personally believe you can't go wrong having extra humidity at hatch, but you most certainly can by having it too low.

These are my thoughts and theories of humidity based on research and experience. I by no means am an expert, but I have hatched some adorable little fuzzy butts with this knowledge.

Amylynn the first part of your post is fantastic! You have nailed it with your clear explanation and graph. The whole post is very informative and relatable. You always give complete info for the new hatchers. You should copy that to any member who has questions about humidity. Thank you for taking the time to write it all down.

A very nice explanation. And I agree, the Learning Center is a great resource.

I’ll just add that there is no perfect humidity for every egg. Some eggs have more porous shells so they lose humidity faster. Some have thicker whites than others, which affects how fast they lose humidity. Some have been stored longer than others. They have been losing humidity while stored so the starting point is not the same.

Some people weight the eggs during incubation to monitor moisture loss. If they weight individual eggs they get readings all over the place. Different eggs are losing moisture at different rates. What you are looking for is not the ideal humidity for each individual egg but the best humidity for the majority of eggs. Instead of weighing the eggs individually, they need to weigh the eggs together and take the average.

The good news about humidity is that there is a wide band that actually works. You don’t have to be spot on. I agree the best thing to do is to pick a humidity and try it. Then when your incubation is over, open any unhatched eggs to see if you can determine what the problem was. There are a whole lot of things that can cause an egg to not hatch, not just humidity. These troubleshooting guides can help you determine what the problem might have been so you can tweak your incubation to maybe get better results in the future. Opening them is going to be gross for some people, but I find it is not nearly as bade as you think once you do it. If you don’t open them, you really don’t have a clue what went wrong.

Amylynn the first part of your post is fantastic! You have nailed it with your clear explanation and graph. The whole post is very informative and relatable. You always give complete info for the new hatchers. You should copy that to any member who has questions about humidity. Thank you for taking the time to write it all down.

Click to expand...

Thank you. It's somethingI have been working on for a new blog so I had it in my docs.

Very good read.
The only thing I would add is weighing as an alternative to candling and checking humidity. Draw a graph for weight upon setting and target weight. If weight during incubation falls below the line, raise the humidity. If it is above the line, it is too high.